In four-cylinder internal combustion engines, there is known an internal combustion engine in which exhaust ports of the cylinders are merged with each other inside the cylinder head and in which cooling water fed from inside the cylinder block to the inside of the cylinder head is led near the merged parts of the exhaust ports formed in the cylinder head, passes through single cooling water outlets, and is discharged to the outside (see Japanese Patent No. 2709815). In this internal combustion engine, the merged parts of the exhaust ports becoming a high temperature in the cylinder head are cooled by the cooling water, so the merged parts of the exhaust ports can be prevented from overheating.
However, when feeding cooling water discharged from the cylinder head to a radiator, to streamline the piping of the cooling water from the cylinder head to the radiator, usually the cooling water outlets of the cylinder head are combined into one. However, when cooling the merged parts of exhaust ports as a whole homogeneously and directing the cooling water to a single cooling water outlet, the structure of the passages of the cooling water in the cylinder head becomes extremely complicated and, as a result, not only does the flow channel resistance of the cooling water increase, but also the problem arises of a greater number of steps and cost for production of the cylinder head.